This invention pertains to a temperature dependent electric current regulator or limiting circuit element for electrical appliances, especially electrically heated appliances which employ a thermo-sensitive circuit switch with an automatic switchable contact pair activated by a predetermined given temperature.
Electrically heated appliances such as, for example, heating pads, electric blankets, coffee makers and similar devices are provided with an electric current regulator which cuts off the current of the electric heating resistors when a given rated temperature has been obtained. The heating resistors are then automatically reconnected with the current source when the temperature drops once again to a preset value. The temperature is held within a given tolerance range on a preselected value by means of a two-point control. The current control switching elements also serve in this design as current limiting switching elements. When the current surge is excessive as, for example, when parts of the appliance heating resistors are shorted, an automatic cutoff takes place.
In order to avoid fire hazard safety regulations usually require that when such a current regulator or current limiter switching element (also designated as thermostat) breaks down, that the associated instrument will automatically cut off when a preset limiting temperature has been reached. It is known to connect in series with the current regulator or limiting switching element, a safety thermostat. This thermostat is adjusted to a given limiting temperature. When the limiting temperature is reached, the circuit of the heat resistors is interrupted, if this function has not already been carried out, by the current control or limiting switching element.
The arrangement and use of two separate switching elements is expensive in terms of material and manufacturing cost. Furthermore, in some devices there is insufficient space for accommodating these elements.